The moving bed reactor referred in this specification is described in International Patent Publication No. WO91/01359. In the reactor, catalyst is charged into the upper portion of the reactor and is drawn off from the lower portion of the reactor, when necessary, even during reactor operation. It may be used in many kinds of liquid-gas reaction processes, for example in hydrodesulfurization of atmospheric distillation residuum from crude oil or vacuum distillation residuum from topped crude oil.
In the moving bed reactor, as shown in the FIG. 4, a two phase fluid consisting of a reactant gas (for example, a hydrogen containing gas) and a liquid reactant enters into the bottom of reactor A, and flowing upward through a catalyst bed B, exits from the top. Wherever necessary, the catalyst is charged into the reactor A through a catalyst charge pipe C provided in the upper portion and is drawn off through draw-off pipe D located above a supporting structure for the catalyst bed.
In the above-mentioned construction, fresh catalyst charged into the upper portion through the catalyst charge pipe C flows downward while catalyzing the desired process reactions, loses catalyst activity, and finally is drawn off as spent catalyst through draw-off pipe D. The catalyst bed B is maintained at a high catalyst activity by charging fresh catalyst to the catalyst bed at a rate which balances the removal rate of spent catalyst having reduced catalyst activity, so that the desired process reactions can proceed effectively even in a small reactor.
Embodiments of a beam supporting structure are shown in FIG. 5, 6, and 7. FIG. 5 is a plan drawing showing the supporting structure for a moving catalyst bed (hereinafter referred to as the supporting structure). FIG. 6 is a sectional drawing showing the section of the supporting structure in line Y--Y of FIG. 5, and FIG. 7 is a enlarged drawing showing the section of the supporting structure in line Z--Z of FIG. 5.
Supporting structure 1 is constructed of a framework assembly formed by radial beams 3 and transverse members 4 between beams 3, and wire mesh layers 5, 6 overlaying the framework, as shown in FIG. 5. As shown in FIG. 5, FIG. 6 and FIG. 7, the framework consists of 8 beams 3 of a high beam height extending radially like spokes towards the upper portion of the reactor from an octagonal center plate 2, and having transverse members 4 between beams 3 to form similar but different sized octagons.
Spacecloth layer 5 and wire mesh layer 6 overlay the assembly. The spacecloth 5 is a woven wire mesh of thick wires, and the wire mesh 6 is of a smaller mesh size than the particle size of the catalyst particles.
The inlet of draw-off pipe D is set above the center plate 2, as shown in FIG. 4. The center plate 2 and beams 3 are interconnected with each other by adequately sized connecting members, for example octagonal connecting member 7, as shown FIG. 6. The supporting structure 10 is connected to the reactor A by the reinforcing ring 8.
As mentioned above, the supporting structure, which comprises a grid-like framework of beams and plate members and wire mesh layers overlaid on the grid-like frame work, has been developed for moving catalyst bed reactors in accordance with the same technical concept as the grid-like supporting structures used for conventional fixed catalyst beds.
However, when, for example, economic factors require an increase in throughput, reactors having a large diameter are required to meet the throughput requirements. As the diameter of the reactor and the volume of catalyst charged to the reactor increases, the size of individual structural members in the supporting structure, and especially the size of the beams, have to be increased to support the weight load of the increased catalyst volume. As the size of individual structural members, and especially the size of the beams, increases, they tend to prevent the fluid from being uniformly distributed into the catalyst bed. As a result, contact between the fluid and the catalyst becomes uneven and variable from region to region in the reactor.
In the beam supporting structures, when a prefabricated polygonal supporting structure is installed into a cylindrical reactor, its individual members have to be modified mechanically to fit the shape of the reactor. However, it is technically very difficult, and requires a lot of manpower and time, to make such mechanical modifications in the field, and installation costs are high.
As mentioned above, a supporting structure having large support members experience problems with uneven distribution of fluid, and require high fabrication and installation costs. Thus, it is expected in the chemical or petroleum industries to provide an improved supporting structure appropriate to a large reactor.
In this connection, the purpose of the present invention is to provide an easily manufacturable and light-weight supporting structure suitable for supporting a moving catalyst bed in a large reactor, while introducing fluid into the catalyst bed in a uniform distribution.
We have found that the increase in weight of the beam supporting structure is caused mainly by the construction of the grid-like framework consisting of beams and plate members. The grid-like framework is designed considering the load of the catalyst bed as a bending stress. These members are required to have a section modulus comparable to the bending stress.
As a result of study and experiments, the inventors have completed the present invention by adopting a shell-like structure to be designed considering the load of the catalyst bed as a membrane stress rather than a bending stress.